This invention is directed to a process for manufacturing dental prosthetics based on ceramics and a shaped body (green body) which may be used in this process.
In general, dental prosthetics are parts placed onto a patient's natural dentition to restore the latter with its natural functions as far as possible. These parts are manufactured in a highly expensive process. First, the dentist has to prepare or extract the part of dentition to be replaced, e.g., a single tooth or several teeth. After making a model, e.g., by preparing an impression using conventional procedures, the dentist or dental technician manufactures the appropriate denture, including crowns, bridges, inlays, and onlays.
In order to provide the dental prosthetics with an aesthetic appearance they may be jacketed with materials which have good mechanical properties and, at the same time, give the color sensation of natural teeth. As the material for jacketing denture or crowns etc., ceramics have proven to be particularly useful.
According to prior art, as the supports for the jacketing metal frameworks are possible which, in addition to the drawback of expensive and costly manufacturing, are intolerable for the patient at least in individual cases. Some of the drawbacks of restoration with metallic frameworks have been circumvented by the use of core materials made of ceramics.
Thus, EP 86,400,781.0 describes a process for manufacturing ceramic restorations such as bridges, crowns, inlays, onlays, etc., wherein initially, a master model is constructed. This model is coated and the thus obtained impression is cast with a special gypsum. A fine-grain oxide-ceramic slip is applied to the demolded gypsum framework, and the gypsum stump immediately withdraws the liquid proportion, and an almost dry mass layer is formed which may be processed quite well to give the desired framework. The obtained framework is sintered with the gypsum stump in a temperature range where shrinkage does not yet occur. In order to achieve high flexural strength, the porous framework is soaked with glass in an infiltration firing.
Here, processing is highly dependent on the dental technician's skill. In addition, subsequent processing of the framework is hardly possible due to its high mechanical strength and toughness.
Duret discloses the use of CAD/CAM methods for the construction and manufacturing of dental restorations. A prepared stump of tooth is recorded in its surrounding from various directions with a video camera. The recordings are digitalized and transferred via a CAD compatible computer in a three dimensional image. The dental restoration sitting to the above mentioned stump can be constructed online and visible on the screen according to models stored in the computer. Then the dental restoration is worked out by a computer assisted micromilling machine from a prefabricated block of the respective materials such as metal or dental ceramics. However, the material used, in the case of dental ceramics, does not show optimum mechanical strength.
DD 261,741 discloses a procedure which also forms inlays consisting of glass ceramic by mechanical treating. The mechanical treating can occur by aid of electro-optical scanning or contact milling. The glass ceramic to be used does not show the high mechanical strength which could be reached with materials known in the art but which materials cannot be treated mechanically with a reasonable expenditure because of their hardness.